Braking device for two-stroke cycle internal combustion engines



Apnl 9, 19517v A. PoRTMA'NN EEAKINC DEVICE EOE Two-STROKE CYCLE INTERNALcoMBusIIoN ENCINEs Enea nec. 1, 195s United States Patent O BRAKINGDEVICE FOR TWO-STROKE CYCLE INTERNAL COMBUSTIGN ENGINES August Portmann,Arhon, Switzerland, assignor to Societe Anonyme Adolphe Saurer, Arbon,Switzerland, a jointstock company of Swiss law Application December 7,1953, Serial No. 396,555

Claims priority, application Switzerland December 18, 1952 s Claims.(ci. 12s-ss) This invention relates to internal combustion engines andmore especially to means for braking two-stroke cycle engines.

In the operation of internal combustion engines of the two-stroke andthe four-stroke cycle types an additional braking effect has beenobtained by so adjusting the control of the intake and the exhaust portsduring brake operation that the compressed cylinder charge is exhaustedat the end of the compression stroke into the exhaust pipe. Thecompression and pumping work raises the driving turning moment of themotor used for braking, but a device of this kind involves the drawbackof developing great noise.

It is for this reason that one has tried in four-stroke cycle engines,when braking, to throttle the exhaust and to obtain in this manner anincrease of the driving turning moment of the engine by an increase ofthe exhaust work. Such a device is more favorable as far as noise isconcerned, and it offers, in addition, the advantage of being able toregulate the braking effect by varying the throttling effect in theexhaust pipe.

I have now found that in the operation of two-stroke cycle enginesprovided with positively controlled exhaust organs at the end of thecylinder facing the combustion chamber, it is possible to obtain asimilarly favorable braking effect, if in the operation of the brake theconx trol of the exhaust organs is adjusted in such a manner that theyare open at least during a considerable part of the compression stroke,while the exhaust conduit is throttled simultaneously by a Valve or thelike.

In the drawings afiixed to this specification and forming part thereoftwo embodiments of a device according to this invention are illustrateddiagrammatically by Way of example.

In the drawings:

Fig. 1 is a vertical section of an internal combustion engine containinga braking device.

Fig. 2 is an axial section of a device according to this invention forthe adjustment of the cam shaft 11 appearing in Fig. 1.

Fig. 3 is a similar view of another embodiment of a device according tothis invention for adjusting the cam shaft.

Fig. 4 is a cross-section on the line IV--lV in Fig. 3.

Figs. 5 and 6 are diagrams illustrating the system of braking an enginein accordance with this invention, and

Fig. 7 is the distribution diagram of the engine shown in Fig. l.

Referring to the drawings and first to Fig. 1, the cylinder 1 embeddedin the engine casing 2 contains the working piston 3 which is drivingthe crank shaft 5 with the aid of the connecting rod 4. The upper edge 6of the piston controls the intake ports 7 of the cylinder. The crankshaft 5 also drives the cam shaft 11 by means of gears 8, 9 and 1i). Thecam 12 of the shaft 11 opens by means of the tappet 13 and lever 14 theexhaust valve 15 against the action of the spring 16. The gear ice 9drives by way of a pinion 17 the scavenging and charging blower 18 whichfeeds air into the receiver 19 and into the cylinder 1 when the ports 7are uncovered by the edge 6 of the piston 3. The valve 15 opens into theexhaust conduits 20 and 21 which are separated by the valve 22. Theexhaust ports of all the cylinders of the engine open into the port 20of the exhaust conduit in front of the shut-olf valve 22. The branchtube 24, opened and closed by the throttling valve 23, connects thepressure side of the scavenging blower 18 with the exhaust conduit 21located behind the cut-off valve 22. The operating lever 25 is connectedby means of the rod 26 with the throttle valve 23 so that while theexhaust valve 22 is closed, the throttle valve 23 is openedapproximately in proportion to the total time-crosssection of theengine. While this engine operates as a motor, the throttling valve 23is closed. This valve might also be designed to act as a safety valveand in that case the rod 26 would be dispensedwith.

The oil pump 35 of the engine communicates by way of the pipe 31 withthe reversing valve 32, from which pipes 33 and 34 lead to one and theother pressure chamber of the piston sleeve of the stationary cylinderswitch 36. The reversing valve 32 is connected by means of the rod 37'with the lever 25 controlling the valve 22 in such a manner thatimmediately the lever 25 has been moved, reversal is eected so that fromthen on until the lever has gone through his full stroke, merely thespring 3S is compressed.

As shown in Fig. 2, one end (42) of the cam shaft 11 is coarselythreaded and is connected by means of the piston sleeve 35 with theshaft 41 which is also formed with a coarse thread. In consequence ofthis, the shaft 11 can be turned through an angle a relative to theshaft 45 by displacing the sleeve piston 35. The gear 10 is keyed ontothe shaft 40.

The hollow piston 35 is held in one or the other position by oilpressure. Of course, oil pressure might also be used to hold the pistonin one position only against the presssure of a spring.

Another way of angular adjustment of the cam shaft 11 relative to thedriving gear 50 is illustrated in Figs. 3 and 4. Here the cam shaft 11carries at its left-hand end an angularly adjustable piston 51 with twovanes 52 and 53 which can be turned one way or the other within thehollow gear 5t). The piston 51 thus subdivides the interior of the gear50 into four compartments 54-57. The hub portion of the piston isperforated in such manner that the compartments 55, 57 communicate viathe annular compartment 58 with the pipe 34, the compartments 54, 56 viathe annular compartment 59 with the pipe 33. Corresponding to thepressure in the pipes 33, 34 the piston 51 and with it the cam shaft areturned through a predetermined angle a relative to the driving gear 55.instead of this, a planet gear might be used, in which the stationarypart could be turned angularly.

in the diagram of Fig. 5 the full line shows the progress of thepressure p in a cylinder of the engine in dependence on the crank anglefp which results when the engine is driven from the outside without asupply of fuel.

In the diagram of Fig. 6 the full lines denote the coordinate times ofopening of the intake ports 7 and exhaust control 15.

The cycle of operation begins with the inward stroke of the piston. Atthe beginning of the stroke the intake ports 7 and the exhaust control15 are open, the cylinder is scavenged. Shortly before the closing ofthe intake ports the exhaust control has been closed so that thecylinder is charged up to the pressure in the receiver. As the pistonthen proceeds inwardly, the air is compressed according to curve a.During the now follownimmer a. di ing outward stroke of the piston theair in the cylinder expands according to curve b. Since the surfacesbelow the curves a and b are of equal or approximately equal size, thebraking effector the l engine merely consists of the frictional work andthe Work required by the scavengingrand charging blower.

If the engine is intended to be used for braking, the exhaust conduit 20is throttled by turning the lever 2S, the fuel supply being shut off,and the reversing valve 32 is so adjusted by means of the rod 37 thatthe oil pressure supplied by the oil pump 30 displaces the sleeve piston3S, thereby so `adjusting the cam shaft 11 that the exhaust valve 15 isopened after the working piston, as line A1 (Fig. 6) shows, has coveredthe intake ports 7. The air now flows along line c from the hrottledexhaust conduit 20 into the cylinder 1, so that the piston 3 is forcedto expel the air along line d against the pressure in the exhaustconduit 20. At the end of the stroke the exhaust control 1S is closed.When the piston 3 now moves outwardly, the air in the cylinder t expandsaccording to curve e Vconsiderably below the pressure in the receiver..Shortly before the end of the stroke the piston 3 uncovers the intakeports 7 and the cylinder 1 is now charged up to the pressure in thereceiver,

In the distribution diagram of Fig. 7 the exhaust control15 is openedduring operation as a motor over the angle ,B and over the angle 'y thepiston 3 uncovers the intake ports 7. During braking the opening periodof the exhaust control 15 is displaced by the angle a..

I wish it to be understood that l do not desire to he limited to thedetails described in the foregoing specifi cation and shown in thedrawings for obvious modifications will occur to a person skilled in theart.

I claim:

1. Braking system for two-stroke cycle internal rcombustion enginescomprising in combination, a cylinder, a piston arranged forreciprocation in said cylinder, an exhaust conduit connected with saidcylinder, an exhaust valve connected with said conduit, means forcontrolling said valve, means for so adjusting the exhaust valve controlthat the valve s kept open during a considerable part of the compressionstroke of the piston and means for simultaneously throttling the exhaustconduit.

2. Braking system for two-stroke cycle internal combustion enginescomprising in combination, a cylinder,

a piston arranged for reciprocation in said cylinder, an exhaust conduitconnected with said cylinder, an exhaust valve connected with saidconduit, a cam shaft controlling said valve, means for so adjusting theangular position of said cam shaft that said valve is kept open during aconsiderable part of the compression stroke of the piston and means forsimultaneously throttling said exhaust conduit.

3. Braking system for two-stroke cycle internal combustion enginescomprising in combination, a cylinder, piston arranged for reciprocationin said cylinder, an exhaust conduit connected with said cylinder, anexhaust valve connected with said conduit, a cam shaft controlling saidvalve, a hollow driving gear operatively connected with said cam shaft,a rotary distributing valve in said gear and means for so adjusting theposition of said valve relative to said gear that said valve is keptopen during a considerable part of the compression stroke of the pistonand means for simultaneously throttling .said exhaust conduit.

4. The braking system of claim 1 in combination with a blower, a pipeleading from the pressure side of Vsaid blower to the exhaust conduit, athrottling device inserted in said pipe and a connection between theexhaust conduit throttling means and said throttling device ar rangedfor opening said device when said throttling means close.

5. The braking system of claim l in combination with a blower, means forconnecting the pressure side of said blower with the exhaustconduit anda safety valve in said connecting means, whereby to pass air from saidside of the blower to the exhaust conduit when due to throttling of saidconduit, the pressure on said side of the blower exceeds a predeterminedvalue.

References Cited in the tile of this patent UNITED STATES PATENTS876,020 Salter Jan. 7, 1908 1,518,799 Krutina u Dec. 9, 1924 1,624,525Beach Apr. 12, 1927 1,829,780 Beytes et al. Nov. 3, 1,931 2,037,051Smiley Apr. 14, 1936 2,148,854 Bokemuller Feb. 28, 1939 2,178,152 WalkerOct. 3l, 1939

